Archive for December 18th, 2013

We recently noticed that there has been an increase in spammed messages that use airline information as bait. These messages are made to look like notifications from airlines such as Delta Airlines, British Airways, US Airways, and American Airlines. Each message comes with an attachment—often in the form of a fake e-ticket—that recipients are supposed to open. This attachment is actually a BKDR_KULUOZ variant.

Figure 1. Screenshot of sample spam

KULUOZ variants are known to download and execute other malware, such as SIREFEF/ZACCESS and FAKEAV variants. KULUOZ variants are also evolving: we’ve even seen one variant, detected as BKDR_KULUOZ.MN, that collect system information including the antivirus installed in the affected computer. This is a routine previously unheard of from this malware family.

While we have seen KULUOZ spam in the past, there have been no significant change in numbers in the past several months. KULUOZ spam now represents nearly half of all malicious spam attachments.

Figure 2. Breakdown of spam attachments over a one-week period

Based on our investigation, this batch of BKDR_KULUOZ is distributed by the Cutwail/Pushdo botnet. Previously, we noted that the said botnet was responsible for sending out Blackhole Exploit kit (BHEK)-like spam that serve UPATRE variants.

Previous instances of KULUOZ spam used shipping and airline notifications as bait. The exclusive use of airline tickets in this new campaign could be a deliberate move, considering people frequently travel over the holidays. Victims may be more inclined to click attachments if they’re actually expecting airline tickets.

Users should remain extremely careful when opening messages. Since most messages are specially crafted to look as legitimate as possible, it’s ideal to double-check with the sender to see if an email is legitimate. Trend Micro Smart Protection Network blocks all related threats in this attack.

Recently Google announced that it had changed its policy dealing with images in email. In a blog post on the official Gmail blog, Google said:

[You’ll] soon see all images displayed in your messages automatically across desktop, iOS and Android. Instead of serving images directly from their original external host servers, Gmail will now serve all images through Google’s own secure proxy servers.

Simply put, this means that all pictures in emails will now be automatically displayed. Instead of being served directly from the site hosting the image, however, they will be given a copy that has been scanned by Google.

Officially, the stated rationale for this change is that previously, senders “might try to use images to compromise the security of your computer”, and that with the change images will be “checked for known viruses or malware”. This change affects users who access Gmail via their browser, or the official iOS and Android apps.

In the past, there have been occasions where malicious images were used to compromise computers. A number of image formats were exploited in 2005 and 2006, including a Windows Metafile vulnerability (MS06-001), and an Office vulnerability that allowed arbitrary code execution (MS06-039). More recently, a vulnerability in how TIFF files were handled (MS13-096) was found and not patched until the December Patch Tuesday cycle. Properly implemented, scanning the images would be able to prevent these attacks from affecting users.

However, actual exploitation of these vulnerabilities has been relatively uncommon. Exploit kits have opted to target vulnerabilities in Flash, Internet Explorer, Java, and Reader instead. Image vulnerabilities are not even listed in the control panels of these kits.

The primary reason to block images is not to block malware, but to stop information leakage. Images are used by spammers and attackers to track if/when email has been read and to identify the browser environment of the user. Email marketers also use this technique to check how effective their email campaigns are.

Email marketers have already confirmed that in spite of Google’s moves, email tracking is still very possible. Google’s proposed solution (a web proxy that checks images for malware images) appears to solve a small security problem (malicious image files), while leaving at risk user’s security and privacy. Attackers still have the capability to track that users have read email–and to learn aspects of their browser environment.

Users can still revert to the previous behavior via their Gmail settings, as outlined in Google’s blog post:

Of course, those who prefer to authorize image display on a per message basis can choose the option “Ask before displaying external images” under the General tab in Settings. That option will also be the default for users who previously selected “Ask before displaying external content”.

We strongly recommend that users change this setting for their accounts. Users who access Gmail via POP3 or IMAP should check the settings of their mail application to control the display of images.